1. Technical Field
The present invention relates to a switching system and method for an asynchronous transfer mode, and more particularly relates to a switching system and method for an asynchronous transfer mode for multimedia service.
2. Background Art
Generally, multimedia communications involve the blending together of computer data processing, audio/video, and display technology in an interactive environment. Multimedia service concerns a variety of traffic characteristics (data rate, burstiness or the like), and service qualities (transfer delay, transfer delay variance, data loss or the like). In addition, its service format requires point-to-point, point-to-multipoint, and multipoint-to-multipoint configurations. In one type of services, there could be single connection and multi-connection. Traditional switching networks such as a public switched telephone network (PSTN) and a packet switched public data network (PSPDN) are not capable of providing multimedia services because they are designed for a specific service of a predetermined format. Therefore, for multimedia services, a switching network of a new format is required, and developments in various services, from terminals to switching/transfer system, forming such a new switching network are necessary. Presently, the most suitable transmission and switching technique which implements multimedia communication combining high quality voice, video, and high speed data traffic is known as Asynchronous Transfer Mode (ATM), an internationally agreed technique adopted by the International Telecommunication Union (ITU) for purposes of standardization of ATM communication networks.
Generally, an ATM switching network decomposes multimedia communication data into fixed length blocks having a predetermined bit size, no matter whether the communication data is voice, image, data or the like. The block is referred to as a cell. The cell includes a header portion and a data portion. In the header portion, destination identifing information or the like is stored. By using this destination identifying information, every information is transmitted and switched in a multiplexed manner at high speed on a cell basis. Conventionally, there are a variety of ATM switching networks. Exemplary configurations are disclosed, for example, in U.S. Pat. No. 4,956,839 for ATM Switching System issued to Torii, U.S. Pat. No. 5,214,642 for ATM Switching System And Adaption Processing Apparatzis issued to Kunimoto, U.S. Pat. No. 5,202,885 for ATM Exchange With Copying Capability issued to Schrodi et al., U.S. Pat. No. 5,258,977 for Switching Network For An Asynchronous Time Division Multiplex Transmission System issued to Wolker et al., U.S. Pat. No. 5,339,310 for Switching Apparatus For Switched Network of Asynchronous Transfer Mode issued to Taniguchi, U.S. Pat. No. 5,410,540 for Shared-Buffer-Type ATM Switch Having Copy Function And Copy Method Thereof issued to Aiki, U.S. Pat. No. 5,455,820 for Output-Buffer Switch For Asynchronous Transfer Mode issued to Yamada, U.S. Pat. No. 5,537,402 for ATM Switch issued to Notani et al., U.S. Pat. No. 5,555,378 for Scheduling Transmission Multimedia Information In Broadhand Networks Using A Token Passing scheme issued to Gelman et al., U.S. Pat. No. 5,557,609 for Switching Apparatus for ATM issued to Shobatake et al. For example, for purposes of dividing information transfer channel, there are time division and space division ATM switching networks. For topology, there are ring type, bus type and lattice type ATM switching networks. In addition, depending on the location of a buffer used, there are a number of ATM switches in the network including an input buffer, common buffer, dispersed buffer, and output buffer. Each ATM switch is referred to as a unit switch.
The space-division ATM switching network basically has a lattice form like a Banyan network or a cross-bar network, and a self-routing in which cells inside the switch network search for their own destination (switch network's output ports) according to its hardware architecture. However, this structure must contain a buffer because most of unit switches involve internal blocking. All ATM switching networks including space division and time division types must also include an output buffer on their respective output sides because of output port collision.
The input buffer included in the space-division ATM switching network can be classified as either a dedicated buffer or a shared buffer, although the dedicated buffer is normally used. Dispersed buffer types are advantageous because of their easy operation. However, they are disadvantageous in that the buffer used for the respective ports of the switch network is fixed and thus the traffic (cells) is not scattered to the switch network ports on the whole. As a result, if the cells are maldistributed, the overflow of input data can occur at any port.
In the ATM switching network, the internal path between an input port and output port can be a single path or multiple paths. In case of single path, internal blocking frequently occurs and this may decrease its performance due to cell loss. In spite of the internal blocking, however, the single-path ATM switching network has a simple internal routing and is easy to operate. In case of the multiple-path switch network, the probability of internal blocking is small but the control of routing for the multiple paths is too complicated to be applied to a large volume of switches. This is because the control speed of the switching network for routing does not reach the cell transfer speed.
In a case that the multiple-path space-division ATM switching network is implemented with a shared buffer as its input buffer, the overflow of input data caused in the dispersed buffer type can be eliminated. However, in the ATM switching network whose transfer speed is hundreds of Mb/s, it is impossible to implement a large volume of switches despite of parallel transfer because its transfer speed is far faster than a memory operation speed. According to current semiconductor technology, the largest implementable size of the switching network is within 8*8 in case of eight-bit parallel data transfer.
As described above, the conventional ATM technique selects an easy-to-implement mode among time division/space division, buffer usage, single path/multiple path in the ATM switching network. However, the conventional ATM switching network, as I have observed, has the following problems.
First, if the ATM switching network is time division, its capacity is so limited due to the limitation of commercially available memory access time. For instance, in an eight-bit parallel ATM switch network, the size of switch network manufactured is 4-8 ports.
Second, if the ATM switching network has multiple paths, the routing paths are multiple from the input port to the output port so that this should be analyzed for every call so as not to cause internal blocking in the switching network. However, this technique requires a very sophisticated control algorithm, and is therefore impossible for implementation as the size of switching network becomes larger.
Third, if the dedicated buffer is implemented as an input buffer allocated for every input port in the space-division input buffer switch network, the probability of overflow of buffer becomes larger according to the input traffic characteristics, causing service quality deterioration due to cell loss. In addition, the buffer utility efficiency is so low that the buffer cost increases in order to satisfy the performance as in the shared buffer mode.